Vehicle hydraulic system

ABSTRACT

A hydraulic system incorporated into a vehicle is provided. The system includes a plurality of actuators for providing a desired configuration of a vehicle. A valve system is operatively coupled to the plurality of actuators for controlling a flow of pressurized fluid to the plurality of actuators to energize the actuators to produce, responsive to the desired configuration of the vehicle, a first configuration of a plurality of first configurations of the vehicle corresponding to the desired configuration of the vehicle, or a second configuration of a plurality of second configurations of the vehicle corresponding to the desired configuration of the vehicle.

BACKGROUND

The present invention relates to vehicles with lean control systems. Inparticular, the present invention relates to vehicles withhydraulically-actuated primary and auxiliary lean control systemscoupled to a vehicle leaning suspension system for enhancing vehiclestability.

Certain types of vehicles are unstable (e.g., more prone to rollingover) in certain modes of operation. For example, a three-wheeledvehicle that permits roll axis articulation may be unstable when thevehicle center of gravity is located above the roll axis. Under normaloperation, many such instabilities are compensated for by using a closedloop control system (for example, an electro-hydraulic orelectro-mechanical system) including or coupled to elements of thevehicle systems (for example, elements of the vehicle suspension system)which are actuatable in response to a signal from a control unit. Basedon feedback to the control unit from vehicle system elements andsensors, signals from the control unit actuate the responsive vehiclesystem elements to stabilize the configuration of the vehicle. Forexample, vehicle lean control systems may cause the body of the vehicleto lean into a turn, thereby increasing the stability of the vehicleduring turning.

In hydraulically-actuated lean control systems, the lean control systemmay fail to function properly in the event of loss of hydraulic control(due to normal system shutdown, vehicle or hydraulic system power loss,hydraulic fluid leakage, etc.) In this instance, it is desirable thatthe vehicle is returned to and maintains an upright (no lean)configuration until hydraulic control can be restored. It is alsodesirable that the configuration of the vehicle, in the absence ofhydraulic control, be as stable as possible.

SUMMARY

In accordance with the present invention, a hydraulic system is providedfor powering a series of actuators which combine to provide a desiredconfiguration of a vehicle. In one embodiment, the hydraulic systemincludes a plurality of actuators for providing the desiredconfiguration of the vehicle. A supply of pressurized fluid is providedfor the plurality of actuators. A valve system is operatively coupled tothe actuators for controlling a flow of the pressurized fluid to theplurality of actuators to energize the actuators to produce, responsiveto the desired configuration of the vehicle, either a firstconfiguration of a plurality of first configurations of the vehiclecorresponding to the desired configuration of the vehicle, or a secondconfiguration of a plurality of second configurations of the vehicle,wherein the first or second configuration provided by the actuatorscorresponds to the desired configuration of the vehicle.

In another aspect of the invention, a hydraulic system is providedincluding a plurality of actuators for combining to provide a selectedconfiguration of a vehicle, the selected configuration of the vehiclecomprising one of a first configuration of a plurality of firstconfigurations, or a second configuration of a plurality of secondconfigurations. A first hydraulic circuit is provided for energizing theplurality of actuators to produce the first configuration of theplurality of first configurations of the vehicle when the firsthydraulic circuit is activated. A second hydraulic circuit is providedfor energizing the plurality of actuators to produce the secondconfiguration of the plurality of second configurations of the vehiclewhen the second hydraulic circuit is activated. A control system isoperatively coupled to the first hydraulic circuit and the secondhydraulic circuit for selectively activating one of the first hydrauliccircuit and the second hydraulic circuit to provide, responsive to atleast one input to the control system, a first configuration of theplurality of first configurations of the vehicle or a secondconfiguration of the plurality of second configurations of the vehicle,wherein the first or second configuration provided by the actuatorscorresponds to the selected configuration of the vehicle.

In yet another aspect of the invention, a hydraulic system is providedincluding a hollow cylinder formed within a housing, and an actuatorslidably positioned within the cylinder and adapted to form asubstantially fluid-tight seal between a first portion of the cylinderproximate a first end of the actuator and a second portion of thecylinder proximate a second end of the actuator. A compressible fluid ispositioned within the first portion of the cylinder between the firstend of the actuator and a first end of the cylinder. A pressurizedhydraulic fluid is positioned within the second portion of the cylinderfor exerting a force on the actuator to compress the compressible fluidpositioned within the first portion of the cylinder.

Other aspects of the invention will become apparent by consideration ofthe detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a three-wheeled motorcycle including aleaning front suspension coupled to an auxiliary lean control systemembodying the present invention.

FIG. 2 is a side view of the three-wheeled motorcycle of FIG. 1.

FIG. 3 is a front view of the three-wheeled motorcycle of FIG. 1,illustrating the three-wheeled motorcycle in an upright position.

FIG. 4 is a front view of the three-wheeled motorcycle of FIG. 1,illustrating the three-wheeled motorcycle in a leaning position.

FIG. 5 is an enlarged perspective view of the front suspension of thethree-wheeled motorcycle of FIG. 1.

FIG. 6 is an exploded perspective view of the front suspension of thethree-wheeled motorcycle shown in FIG. 5.

FIG. 7 is a graphical representation of a potential energy functiondescribing the vehicle state during operation of a primary lean controlsystem of the vehicle.

FIG. 8 is a graphical representation of a potential energy function ofan auxiliary lean control system operable upon deactivation ormalfunction of the primary lean control system.

FIG. 9 is an exploded perspective view of one embodiment of theauxiliary lean control system for the three-wheeled motorcycle of FIG.1.

FIG. 10 is a partial cross-sectional view of the auxiliary lean controlsystem of FIG. 9 with the three-wheeled motorcycle in a leaningposition.

FIG. 11 is a view similar to FIG. 10, with the three-wheeled motorcyclein an upright position.

FIG. 12 shows a resultant potential energy function derived by applyingthe energy stored in the auxiliary lean control system shown in FIG. 9to the vehicle system, effectively combining the potential energyfunction shown in FIG. 8 with the potential energy function shown inFIG. 7.

FIG. 13 is a schematic illustrating a hydraulic system for actuating theprimary and auxiliary lean control systems of the three-wheeledmotorcycle of FIG. 1.

DETAILED DESCRIPTION

Before any embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangement of components set forthin the following description or illustrated in the following drawings.The invention is capable of other embodiments and of being practiced orof being carried out in various ways. Also, it is to be understood thatthe phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” or “having” and variations thereof herein ismeant to encompass the items listed thereafter and equivalents thereofas well as additional items. Unless specified or limited otherwise, theterms “mounted,”“connected,” “supported,” and coupled and variationsthereof are used broadly and encompass both direct and indirectmountings, connections, supports, and couplings. Further, “connected”and “coupled” are not restricted to physical or mechanical connectionsor couplings. Also as used herein, the “lean angle” of the vehicle isdefined as the angle at which a tiltable or leanable portion of thevehicle leans with respect to a road or other surface on which thevehicle rests.

FIGS. 1 and 2 illustrate a three-wheeled motorcycle or trike 10 havingan engine 12, handlebars 14, a frame 16, a single rear wheel 20, firstand second front wheels 22, 24, and an auxiliary lean control system 26.The rear wheel 20 is rotatably mounted to a rear portion of the frame16, and the front wheels 22, 24 are coupled to the frame 16 via aleaning suspension system 18. The frame 16 includes a front bulkhead 40and a main bulkhead 42 defining the front portion of the frame 16. Thefront bulkhead 40 is connected to the main bulkhead 42 to stiffen andstrengthen the entire suspension system 18. The engine 12 is coupled tothe rear wheel 20 through a drive assembly (not shown) to propel thetrike 10. The handlebars 14 are pivotally coupled to the front portionof the frame 16 and coupled to the front wheels 22, 24 through asteering system to controllably turn the front wheels 22, 24.

The illustrated embodiment is for a trike 10 having two steerable frontwheels 22, 24 and a single, driven rear wheel 20. It should be notedthat it is within the scope of the invention to employ the suspensionsystem and lean control systems of the present invention in a vehiclehaving two rear wheels and a single front wheel. Also, in otherembodiments, the suspension system and lean control systems can be usedfor the front wheels, the rear wheels, or both the front and rear wheelsin a vehicle having four wheels, such as an ATV.

FIG. 3 illustrates a front view of the trike 10 of FIG. 1, showing theleaning suspension system 18 in an upright position. This positionillustrates the orientation of the suspension system 18 while the trike10 tracks a straight line on a flat surface. FIG. 4 illustrates thefront view of the trike 10 in a leaning configuration. This view showshow the suspension system 18 is oriented when the trike 10 is turning,or tracking an arcuate path. It should be noted that in order tohighlight the different positions of the suspension system 18 betweenFIGS. 3 and 4, the handlebar 14 and wheel 22, 24 positions areillustrated in the same center straightforward position for both FIGS. 3and 4. Although this position is correctly illustrated in FIG. 3 thehandlebar 14 position and the wheel 22, 24 positions in FIG. 4 should hepivoted and turned, respectively, toward or into the direction of theturn.

As used herein, the term “leaning suspension system” is defined as asuspension system that permits and/or facilitates leaning of a portionof the vehicle, wherein the leaning is initiated in response to forcesexerted on the vehicle during turning of the vehicle by an active orpassive lean control system installed in the vehicle.

FIGS. 5 and 6 illustrate a perspective view and an exploded perspectiveview of the leaning suspension system 18, respectively. The leaningsuspension system 18 includes a transverse beam 30, upper control arms32, lower control arms 34, spring dampers 36, and spindles 44. Thespindles 44 each include upper and lower pins 102, 100, as well as meansfor rotatably coupling to one of the front wheels 22, 24, such as a hole101 for receiving a wheel axle 103. The structure of the spindle 44 iswell known to those skilled in the art.

The transverse beam 30 is rigid and remains substantially horizontalduring operation of the trike 10. The transverse beam 30 has a centerpivot point 60, end pivot points 62, and intermediate pivot points 64.In the embodiment shown in FIGS. 5 and 6, transverse beam 30 ispivotally coupled to a portion of the main bulkhead 42 at the centerpivot 60 using a keyed shaft 61 (FIG. 9). However, other methods ofcoupling beam 30 to main bulkhead 42 are also contemplated. The centerpivot 60 is positioned to coincide with a longitudinal centerline of thetrike 10 and defines a pivot axis that is parallel to the vehiclecenterline. The end pivot points 62 are pivotally coupled to upperpivots 70 on the spring dampers 36.

The lower control arms 34 have trunnions 80 rotatably coupled to one endand adapted to rotatably receive the lower pin 100 on the spindles 44.These trunnions 80 allow the suspension to operate independent of wheelsteering by permitting the spindles 44 to pivot and turn regardless ofthe position of the lower control arms 34. The two remaining ends of thelower control arms 34 include front and rear pivot points 82, 84 thatare pivotally connected to the main bulkhead 42. Central pivot 86 islocated centrally on the lower control arms 34 and is adapted topivotally couple to lower pivot points 72 on the spring dampers 36.

The upper control arms 32 also have trunnions 80 rotatably coupled toone end adapted to rotatably receive the upper pin 102 on the spindles44. These trunnions 80 allow the suspension to operate independent ofwheel steering. The two remaining ends of the upper control arms 32include front and rear pivot points 90, 92 that are pivotally connectedto the main bulkhead 42.

In the illustrated embodiment, the transverse beam 30 is positionedbetween the front and rear pivots 90, 92 on the upper control arms 32.In other embodiments, the transverse beam 30 could be positioned infront of the front pivots 90, behind the rear pivots 92, or coupled to adifferent location than the upper control arms 32 (i.e. coupled to adifferent bulkhead).

As mentioned above, the spring dampers 36 include upper and lower pivotpoints 70, 72 connecting the transverse beam 30 to the lower controlarms 34. The spring dampers 36 include a shock-absorbing membersurrounded by a biasing member. This style of spring damper 36 is wellknown to those skilled in the art, and will not be discussed in furtherdetail. Alternative embodiments may utilize a different method ofbiasing and shock absorbing, such as leaf springs, coil springs, or airsprings.

Referring again to FIG. 6, the substantially horizontal orientation ofthe transverse beam 30 is maintained by the influence of the springdampers 36. The lower control arms 34 are connected to the front wheels22, 24 through the spindles 44 and to the transverse beam 30 by thespring dampers 36. The front wheels 22, 24, and thus the lower controlarms 34, remain substantially parallel to the road during normaloperation. The road is generally substantially planar for the width ofthe trike 10, meaning that as long as both front wheels 22, 24 are incontact with the road, whether cornering or tracking a straight line,the spring dampers 36 will bias the transverse beam 30 to an orientationsubstantially parallel to the road.

The steering system includes spindles 44, tie rods 46, and the steeringbox 48. The handlebars 14 are coupled to the steering box 48 such thatwhen an operator turns the handlebars 14, an output shaft (not shown) onthe steering box 48 rotates. The output shaft is pivotally coupled to afirst end of each tie rod 46. The second end of each tie rod 46 ispivotally coupled to one of the spindles 44. As the output shaft on thesteering box 48 rotates, the tie rods 46 follow, pulling one spindle 44and pushing the other. The spindles 44 are rotatably coupled to theupper and lower control arms 32, 34 by upper and lower pins 102, 100.Thus the pushing or pulling action initiated by the tie rods 46 causesthe spindles 44, and thus the front wheels 22, 24, to rotate about theupper and lower pins 102, 100.

A hydraulically-energized primary lean control system affects aconfiguration of the vehicle, specifically the attitude or orientationof vehicle bulkheads 40 and 42 with respect to the ground on which thevehicle rests. Referring again to FIG. 6, the primary lean controlsystem includes hydraulic actuators 38, 39 having upper and lower pivotpoints 110, 112, respectively. It is understood that actuator 38 ispositioned on an opposite side of vehicle bulkheads 40, 42 from actuator39 and is, therefore, not visible in FIG. 6. The illustrated embodimentshows the upper pivot points 110 of the hydraulic actuators 38, 39 arepivotally coupled to respective intermediate pivot points 64 on thetransverse beam 30 at a location between the center pivot point 60 andone of the end pivot points 62. Other embodiments could include thehydraulic actuators 38, 39 pivotally coupled to respective end pivotpoints 62 and the spring dampers 36 pivotally coupled to the transversebeam 30 at a location between the center pivot point 60 and a respectiveone of the end pivot points 62. The hydraulic actuators 38, 39 andspring dampers can also be pivotally coupled to other points along thetransverse beam 30.

In a manner explained in greater detail below, the hydraulic actuators38, 39 act to control the orientation of the trike 10 during normalvehicle operation. When entering a turn, one of the hydraulic actuators38, 39 extends in length while the other retracts, moving the trike 10into a leaning position as illustrated in FIG. 4. When the trike 10 isleaving the turn, the hydraulic actuators 38, 39 act to bring the trike10 back to a vertical or upright orientation as illustrated in FIG. 3.

As stated previously, upon failure, deactivation, or malfunctioning ofthe primary lean control system, it is desirable that the vehicle isreturned to and maintains an upright (no lean) configuration untilhydraulic control can be restored. It is also desirable that thisupright configuration of the vehicle, in the absence of hydrauliccontrol, be as stable as possible.

Instability in the configuration of the vehicle may be characterized asa relatively greater amount of potential energy stored within theconfiguration of the vehicle system. FIG. 7 is a graphicalrepresentation of a potential energy function describing the vehiclestate during operation of the primary vehicle lean control system. InFIG. 7, the stability is expressed as a potential energy function of thevehicle system in a static case (i.e., when the vehicle velocity iszero), with a lower system potential energy reflecting a more stableorientation of the vehicle. In FIG. 7, the potential energy of thevehicle system is shown as a function of the lean angle of the vehicleprovided by the vehicle lean control system. As seen in FIG. 7, thepotential energy of the vehicle system is relatively lower at greaterlean angles, due to a shift of the vehicle center of gravity to aposition of lesser elevation. In contrast, a relatively less stablevehicle configuration is represented in FIG. 7 by a relative maximumpotential energy of the system, which occurs when the vehicle is in theupright or on-center position. At a lean angle of zero degrees (i.e.,when the vehicle is in an upright position), the vehicle center ofgravity is at its highest point, and the vehicle system potential energyis relatively high.

In view of the above, upon failure, malfunction, or deactivation of theprimary lean control system, it is desirable to achieve a predeterminedvehicle lean angle which is closest to an upright position of thevehicle and at which the vehicle system has a relatively low potentialenergy. In the present invention, this is accomplished by employing anauxiliary lean control system which brings the vehicle body to adesired, predetermined lean angle upon failure, malfunction, ordeactivation of the primary lean control system. In general, the energyapplied by the auxiliary lean control system to adjust the lean angle toa predetermined value necessary for maximum stability will depend on thedifference between the current lean angle of the vehicle and the desiredpredetermined lean angle of the vehicle. The auxiliary lean controlsystem stores a quantity of energy sufficient to return a portion of thevehicle to the desired predetermined lean angle for stability.

In a particular embodiment illustrating the principles of the presentinvention, it is desirable that the vehicle system have a relatively lowpotential energy when the vehicle is in an upright position (i.e., whenthe vehicle has a lean angle of approximately zero) and resting on asubstantially flat surface. FIG. 8 is a graphical representation of apotential energy function of an auxiliary lean control system inaccordance with the present invention. FIG. 8 illustrates the energyinput into the vehicle system by the auxiliary lean control system toadjust the lean angle of a portion of the vehicle to approximately zero,as a function of the lean angle of the portion of the vehicle when theprimary lean control system becomes inactive. As seen in FIG. 8, thepotential energy input by the auxiliary lean control system is greatestat the largest vehicle lean angle shown because the greater thedifference between the existing vehicle lean angle and the desiredpredetermined lean angle for vehicle stability (in this case zerodegrees), the greater the energy that must be expended by the auxiliarysystem in returning the vehicle to the desired predetermined lean angle.

The force required to adjust the vehicle lean angle (or other vehicleorientation parameter) can be transmitted to the suspension system viaany of a variety of known alternative means (for example, using a crankmechanism). The actual structure utilized will depend on the specificsof the application and the interface of the articulation systemhydraulics.

FIG. 9 is an exploded view of one embodiment of an auxiliary leancontrol system 26 in accordance with the present invention, coupled totransverse beam 30. Auxiliary lean control system 26 generally includesan energy storage device for storing energy to actuate the lean controlsystem, a stabilizing mechanism coupled to the energy storage device andto the leanable portion of the vehicle for applying energy received fromthe energy storage device to the leanable portion of the vehicle, and alinkage coupled to the energy storage device and to the stabilizingmechanism for transferring energy from the energy storage device to thestabilizing mechanism.

In the embodiment shown in FIG. 9, the energy storage device comprises apower cylinder 132 coupled to a portion of the main bulkhead 42 belowthe frame 130, the linkage comprises a shaft 134, and the stabilizingmechanism comprises a roller assembly 136 and a cam 138. A frame 130 iscoupled to a portion of the main bulkhead 42 adjacent the transversebeam 30 and includes two parallel plates 140 extending vertically from abase 142. The plates 140 are substantially identical, but one of theplates includes a clearance cut 148 to allow full rotation of an anglesensor 150 connected to the cam 138. Both plates 140 define a centralaperture 144 aligned with the center pivot point 60 of the transversebeam 30 and a guide slot 146 for the roller assembly 136. The centralaperture 144 defined by each plate 140 is adapted to rotatably supportthe keyed shaft 61 using a bushing 152. The guide slot 146 extendsvertically below the central aperture 144, and provides a limiting pathof travel for the roller assembly 136.

The power cylinder 132 is coupled to a portion of the main bulkhead 42below the frame 130, and is coupled to the base 142 of the frame 130.The power cylinder 132 includes a housing 154, first and secondcylinders 156, 158, a piston 160 movable inside the first cylinder 156,and a cap 162 sealing the second cylinder 158. The cylinders 156, 158are in fluid communication through an aperture (not shown) at the bottomof the cylinders 156, 158. The circumference of the piston 160 forms aseal with the inner wall of the first cylinder 156. The volume of thefirst cylinder 156 above the piston 160 is in fluid communication with ahydraulic system 200 of the trike 10, and the second cylinder 158 (andthus the volume of the first cylinder 156 below the piston 160), isfilled with a compressible fluid, such as a pressurized gas. Althoughthe energy source for the embodiment of the auxiliary lean controlsystem described herein comprises a compressible fluid, alternativeenergy sources are also contemplated, for example, a hydraulicsub-system or a spring system.

The shaft 134 is coupled to the piston 160 at a first end, and coupledto the roller assembly 136 at a second end, such that linear movement ofthe piston 160 along an axis defined by the first cylinder 156 willcause the roller assembly 136 to move in the same fashion.

The power cylinder 132 includes a hydraulic port 164, a pressure sensor166, and a gas fitting 168. The hydraulic port 164 allows the firstcylinder 156 to be placed in fluid communication with the hydraulicsystem 200 of the trike 10. The pressure sensor 166 allows the pressurein the first cylinder 156 to be monitored by the electronic controlsystem. The gas fitting 168 allows the second cylinder 158 to be filledwith the pressurized gas.

The roller assembly 136 includes three individual rollers 174, 176connected by a roller shaft 170. A roller body 172 is coupled to thesecond end of the shaft 134 and is adapted to rotatably support theroller shaft 170. The rollers 174 at the ends of the roller shaft 170move within the guide slots 146 in the frame 130. The center roller 176is adapted to move toward the cam 138 when the piston 160 moves upwardin the first cylinder 156, and move away from the cam 138 when thepiston 160 moves downward in the first cylinder 156.

The cam 138 includes a central aperture 178, a roller recess 180, andtwo protruding lobes 182. The keyed shaft 61 extends through theaperture 178 to support the cam 138 between the two parallel plates 140of the frame 130. The roller recess 180 is positioned between theprotruding cam lobes 182, and has a profile matching that of the centerroller 176. The lobes 182 are angularly offset from each other, andinclude substantially identical inner profiles adapted to engage thecenter roller 176.

FIG. 13 is a schematic illustrating one embodiment of a hydraulic system200 for powering the primary and auxiliary lean control systems toproduce a desired configuration of the vehicle defining a desiredvehicle lean angle.

As used herein, the term “configuration” as applied to the vehicle (or aportion thereof) refers to a particular arrangement of the parts orelements of the vehicle. For example, a first configuration of thevehicle may comprise the particular arrangement of the vehicle elementswhen a portion of the vehicle resides at a first lean angle, while asecond configuration of the vehicle comprises a particular arrangementof the vehicle elements when the portion of the vehicle resides at asecond lean angle different from the first lean angle. Stated anotherway, the vehicle has a different configuration at each differentleftward lean angle and at each different rightward lean angle.

The basic components of hydraulic system 200 include actuators forproviding the desired configuration of the vehicle, a supply ofpressurized fluid for the actuators, and a valve system operativelycoupled to the actuators for controlling a flow of the pressurized fluidto the plurality of actuators. When a portion of the vehicle is to beleaned a desired amount to the right, the valve system controls the flowof pressurized fluid to the actuators to produce a first configurationof a plurality of first configurations of the vehicle corresponding tothe desired configuration of the vehicle. In this case, the plurality offirst configurations of the vehicle comprises a range of rightward leanangles, and the desired configuration is the particular right lean angleof the vehicle determined to be necessary according to the currentmovement conditions of the vehicle. Similarly, when a portion of thevehicle is to be leaned a desired amount to the left, the valve systemcontrols the flow of pressurized fluid to the actuators to produce asecond configuration of a plurality of second configurations of thevehicle corresponding to the desired configuration of the vehicle. Inthis case, the plurality of second configurations of the vehiclecomprises a range of leftward lean angles, and the desired configurationis the particular left lean angle of the vehicle determined to benecessary according to the current movement conditions of the vehicle.Thus, the configuration of the vehicle is adjusted in response to theconfiguration needed to provide the desired lean angle.

Referring to FIG. 13, hydraulic system 200 includes a pump 201 forproviding a supply of pressurized hydraulic fluid to the system, afilter 202, a plurality of proportional control valves PCV1-PCV4, acentering enable valve 206, a centering valve 204 including auxiliarylean control system power cylinder 132, and hydraulic actuators 38, 39(previously described).

In the particular embodiment shown in FIG. 13, filter 202, proportionalcontrol valves PCV1-PCV4, centering enable valve 206, and centeringvalve 204 are all integrated into a unitary valve block, generallydesignated 400. This arrangement reduces valve leakage, greatlysimplifies installation and maintenance of these portions of thehydraulic system, and greatly reduces the amount of connective tubingneeded for interconnecting the various elements of the hydraulic system.

In the embodiment shown in FIG. 13, fluid is circulated from a reservoir220 through hydraulic system 200 by pump 201. Pump 201 is a continuousflow pump (for example, a fixed positive-displacement pump). Hydraulicfluid is routed along various internal passages within valve block 400in accordance with the states (i.e., totally open or closed, partiallyopen or closed, etc.) of proportional control valves PCV1-PCV4,centering valve 204, and centering enable valve 206. The states ofvalves PCV1-PCV4 are set by output signals from an electronic controlunit (ECU) 217 responsive to inputs from various vehicle sensors, asdescribed in greater detail below.

A pressure filter or strainer 202 is provided for filtering impuritiesfrom the hydraulic fluid prior to fluid entry into valve block 400. Inthe embodiment shown in FIG. 13, the filter media is incorporated intovalve block 400. Alternatively, filter 202 may be incorporated into thehydraulic system between pump 201 and valve block 400, or the filter maybe installed in reservoir 220.

In the embodiment shown in FIG. 13, proportional control valvesPCV1-PCV4 are solenoid-actuated spool valves adapted for controlling thespeed and direction of hydraulic fluid flowing through valve block 400.Alternatively, depending on the force requirements of a particularapplication, pilot-solenoid valves may be used. As is known in the art,this type of valve uses a solenoid to control the flow of a pressurizedfluid which powers an actuator that shifts the main flow-directingelement of the valve.

The four proportional pressure control valves PCV1-PCV4, control fluidflow and pressure to the hydraulic actuators 38 and 39. In theembodiment shown in FIG. 13, PCV1 and PCV4 are controlled together andPCV2 and PCV3 are controlled together. This configuration permitscontrol of actuators 38 and 39 using only two electronic drivers.

Each of valves PCV1-PCV4 receives a control signal from electroniccontrol unit (ECU) 217. In the embodiment shown in FIG. 13, each ofvalves PCV1-PCV4 is normally open. Thus, a control current generated by(or controlled by) ECU 217 is applied to the solenoid of each valve toconstrict one or more respective fluid flow paths through the valve, toa degree proportional to the applied current. In the spool valves usedin the described embodiment, the displacement of the spool controllingopening and closing of the flow paths will be proportional to theapplied current. As the valves are proportional control valves, the flowpath through each valve may be constricted to any desired degree by theapplication of a proportionate current to an associated solenoid.

FIG. 13 also shows a hydraulic circuit configured for synchronizedcontrol of two hydraulic actuators 38, 39. However, a hydraulic systemas described herein could incorporate additional fluid control elements(for example, additional valves) for coordinated or integrated controlof corresponding additional hydraulically-actuated elements (forexample, cylinders, rotary actuators, bladder actuators, vane actuators,etc.), depending on the design requirements of the system.

Although the present embodiment utilizes a control system includingsolenoid valves actuated by an electronic control unit, alternative flowcontrol systems may be used. For example, the flow control valves may beactuated mechanically or hydraulically, rather than electrically.Similarly, the valve controller may operate pneumatically orhydraulically, rather than electronically.

In the embodiment shown in FIG. 13, hydraulic actuators 38, 39 areconventional double-acting cylinders. Referring again to FIG. 6,hydraulic actuators 38, 39 include top fluid chambers 210, 211 andbottom fluid chambers 212, 213, respectively. In actuator 38, fluidchambers 210 and 212 are defined by a movable piston 214 rigidlyconnected to a shaft 216, while in actuator 39, fluid chambers 211 and213 are defined by a movable piston 215 rigidly connected to a shaft218. It is understood that actuator 38 is positioned on an opposite sideof vehicle bulkheads 40, 42 from actuator 39 and is, therefore, notvisible in FIG. 6. However, it is also understood that cylinder 38 isstructurally substantially identical to cylinder 39, and that bothcylinders operate in the substantially the same manner. Although theembodiment shown in FIGS. 6 and 13 utilizes double-acting cylinders,other types of actuators may be used in place of (or in addition to)cylinders 38, 39, depending on the application. For example, rotaryactuators, bladder actuators, vane actuators, etc., are alsocontemplated.

Referring again to FIGS. 6 and 13, the hydraulic actuators 38, 39 havetop and bottom fluid ports 114, 116. Piston 214 is provided at the endof shaft 216 within cylinder 38, and piston 215 is provided at the endof shaft 218 within cylinder 39. When hydraulic fluid is forced into thetop fluid port 114 (into either of top fluid chambers 210, 211) byhydraulic pump 201, the associated piston 214 or 215 is forced down, andthe associated shaft 216 or 218 retracts. While this is happening,hydraulic fluid is being forced out of the bottom fluid port 116 (i.e.,out of either of bottom fluid chambers 212, 213) and into reservoir 211.When hydraulic fluid is forced into the bottom fluid port 116, theassociated piston 214 or 215 is forced up, and the associated shaft 216or 218 extends. While this is happening, hydraulic fluid is being forcedout of the top fluid port 114 and into the reservoir.

The hydraulic system is controlled by an electronic control unit orsystem (ECU) 217. ECU 217 generates, responsive to the desiredconfiguration of the vehicle, a control signal for controlling thevalves to control the flow of the pressurized fluid so as to achieve thedesired vehicle configuration, or lean angle. The general configurationof the electronic control unit is known in the art. In one embodiment,the electronic control unit of the present invention comprises aprogrammable digital computing apparatus having a processor, ROM, RAMand I/O apparatus coupled to sensor elements (not shown) and actuatableelements of the vehicle. The electronic control unit stores and runs acontrol program while the vehicle is in use. The sensor elements supplycontrol-related data to ECU 217. The ECU receives input signals from thevehicle sensors (for example, signals indicative of vehicle road speed,the steering angle of the trike handlebars, etc.) and delivers outputcontrol signals to the actuatable elements of the vehicle responsive tothe input signals. Examples of ECU outputs include a current forenergizing a solenoid used to actuate one or more of valves PCV1-PCV4,or a control signal resulting in the supply of suitable currents to thesolenoids. As in known in the art, the control signals transmitted byECU 217 to the valves may be pulse-width modulated to overcome theeffects of stiction on the spool. Alternatively, electronic ditheringmay be utilized to reduce or eliminate stiction effects. A typicalcontrol unit is described in U.S. Pat. No. 6,564,129, incorporatedherein by reference.

Referring again to FIG. 13, a hydraulic system failure may occur inwhich hydraulic fluid is trapped in the hydraulic lines between eitherhydraulic actuator chambers 210 and 213, or in the hydraulic linesbetween actuator chambers 211 and 212. This could occur if, for example,the ECU 217 malfunctions and doesn't allow valves PCV3 or PCV4 to open.In this case, the hydraulic actuators 38, 39 may become locked inwhatever their current state is, thereby possibly locking the trike in aleaning position. This would prevent the auxiliary lean control system26 from operating, as the auxiliary lean control system would beincapable of exerting enough force to overcome the force exerted on thetransverse beam 30 by the trapped hydraulic fluid.

To prevent this, a centering enable valve 206 is provided. During normaloperation, centering enable valve 206 is energized to operationallyisolate the portion of the hydraulic system supplying fluid to actuators38, 39 (i.e., the upstream portion of the system) from the portion ofthe hydraulic system returning fluid to the reservoir from the actuators(the downstream portion of the system). In the event of system pressureloss or controller malfunction, centering enable valve 206 isde-energized and opens when the centering valve 204 is opened to linkthe two hydraulic circuits. This permits the pressure across the workingvolumes of the left and right actuators 38 and 39 to equalize andprevents any hydraulic fluid from getting trapped between the hydraulicactuators 38, 39. This prevents hydraulic lock and enables the auxiliarylean control system to lift the bike to the upright condition, in amanner described below.

Referring to FIGS. 9-11 and 13, power cylinder 132 (previouslydescribed) is coupled to hydraulic system 200. Specifically, the volumeof the first cylinder 156 above the piston 160 is in fluid communicationwith a hydraulic system 200 and is filled with hydraulic fluid, and thesecond cylinder 158 (and thus the volume of the first cylinder 156 belowthe piston 160) is filled with a compressible fluid, such as apressurized gas.

Various other elements may be incorporated into hydraulic system 200,based on the requirements of a particular design or application. Forexample, a temperature sensor 210 may be incorporated into either thehydraulic system reservoir 220 or elsewhere in the system. A temperatureswitch (not shown) may be coupled to the hydraulic system ECU 217 fordeactivating the hydraulic system if the hydraulic fluid reaches acritical temperature, to help prevent damage to the system components.Similarly, a level switch (not shown) may be wired into the hydraulicsystem for deactivating the hydraulic system if the hydraulic fluidlevel drops to a predetermined level, to help prevent damage to thesystem components.

In applications where fluid reservoir 220 is exposed to lowtemperatures, the hydraulic fluid may become too viscous to be drawninto pump 201 without warming. In this case, a thermostaticallycontrolled heater (not shown) may be coupled to the hydraulic systemcontrol for warming the fluid to a predetermined temperature prior toactivation of the hydraulic system.

A pressure sensor 208 may be coupled to the hydraulic system to detectan excessive system pressure condition. One or more pressure sensors 208may be operatively coupled to a pressure relief valve (not shown) toautomatically actuate the relief valve when a predetermined systempressure is exceeded. Alternatively, the pressure sensor(s) may beoperatively coupled to ECU 217, which provides an activation signal to arelief valve upon detection of the excessive system pressure condition.

A heat exchanger (not shown) may also be incorporated into hydraulicsystem 200 to enable extraction of excess heat from the hydraulic fluid.The heat exchanger may have a conventional single or multiple-passconfiguration designed to cool the hydraulic fluid using water or air,as known in the art. The heat exchanger may be mounted to an exteriorportion of the vehicle, or to a portion of the vehicle (for example, aradiator) exposed to an airstream flowing around the vehicle duringmotion of the vehicle, to maximize convective heat transfer from thedevice. To reduce exposure of the heat exchanger to high fluidpressures, the heat exchanger may be positioned along the tank returnline. A bypass valve or relief valve (not shown) can be utilized toprotect the unit from pressure surges. A bypass valve may also bespecified based on fluid temperature, enabling the fluid to bypass theheat exchanger until the fluid has reached a predetermined temperature.The bypass valve then closes and fluid is routed through the heatexchanger. If desired, a thermostatically controlled valve may beinstalled in the hydraulic system to route hydraulic fluid to the heatexchanger if the fluid becomes heated to a predetermined thresholdtemperature.

Operation of hydraulic system 200 in controlling the primary leancontrol system will now be discussed with reference to FIGS. 4, 6, and13.

The pressurized hydraulic fluid supplied to the system 200 by the pump201 passes through the filter 202 first to remove any contaminants.After passing through the filter 202, hydraulic fluid is supplied tovalves PCV1, PCV2, and centering valve 204.

As stated previously, the hydraulic actuators 38, 39 act to control theconfiguration of the trike 10 during normal vehicle operation. Morespecifically, when entering a turn, one of the hydraulic actuators 38,39 extends in length while the other retracts, moving the trike 10 intoa leaning position as illustrated in FIG. 4. When the trike 10 isleaving the turn, the hydraulic actuators 38, 39 act to bring the trike10 back to a vertical orientation as illustrated in FIG. 3.

First, to cause the trike 10 to lean to the right, valves PCV1 and PCV4are closed while PCV2 and PCV3 are opened. This situation permits thepumping of fluid through PCV2 and into hydraulic actuator chambers 211and 212. This will cause the left actuator 38 to extend in length whilethe right actuator 39 retracts. At the same time, fluid from hydraulicactuator chambers 210 and 213 is forced out of the hydraulic actuators38, 39 by the associated pistons 214, 215. The fluid exiting thechambers 210, 213 is forced through open valve PCV3 and to the reservoir220.

Valves PCV2 and PCV3 are opened to a degree necessary to pressurizechambers 211 and 212 such that actuator 38 extends and actuator 39contracts to provide the desired rightward lean angle to a portion ofthe trike. As PCV2 and PCV3 are proportionally energized, the fluid flowis restricted upstream of PCV2 and PCV3, enabling pistons 214, 215 to bemoved to the desired positions within actuators 38, 39, and enabling theforces acting on pistons 214, 215 to be balanced to maintain the pistonsin their desired positions. As the current is reduced in valves PCV2 andPCV3, the pressure differential in the hydraulic system is reducedreducing the restriction of fluid flow to reservoir 220 through port T.This allows the lean control system to reduce lean or return the portionof the trike to a centered configuration.

As previously described, a substantially horizontal orientation of thetransverse beam 30 is maintained by the influence of the spring dampers36. The lower control arms 34 are connected to the front wheels 22, 24through the spindles 44 and to the transverse beam 30 by the springdampers 36. The front wheels 22, 24, and thus the lower control arms 34,remain substantially parallel to the road during normal operation. Theroad is generally substantially planar for the width of the trike 10,meaning that as long as both front wheels 22, 24 are in contact with theroad, whether cornering or tracking a straight line, the spring dampers36 will bias the transverse beam 30 to an orientation substantiallyparallel to the road. The hydraulic actuators 38, 39 connect the frame16 to the transverse beam 30, and control the lean of the trike 10. Asthe hydraulic actuators 38, 39 extend, they push the frame 16 away fromthe transverse beam 30, initiating lean. The biasing force from thespring dampers 36 acting on the transverse beam creates a larger momentabout the central pivot 86 than the hydraulic actuators 38, 39, soextension of the hydraulic actuators 38, 39 moves the frame 16 withrespect to the beam 30.

In the second condition, causing the trike 10 to lean to the left,valves PCV2 and PCV3 are closed while PCV1 and PCV4 are opened. Thissituation permits the pumping of fluid through PCV1 and into hydraulicactuator chambers 210 and 213. This will cause the right actuator 39 toextend in length while the left actuator 38 retracts. At the same time,fluid from hydraulic actuator chambers 211 and 212 is forced out of thehydraulic actuators 38, 39 by the associated pistons 214, 215. The fluidexiting the chambers 211, 212 is forced through open valve PCV4 and tothe reservoir 220.

Valves PCV1 and PCV4 are opened to a degree necessary to pressurizechambers 210 and 213 such that actuator 39 extends and actuator 38contracts to provide the desired leftward lean angle to a portion of thetrike. As PCV1 and PCV4 are proportionally energized, the fluid flow isrestricted upstream of PCV1 and PCV4, enabling pistons 214, 215 to bemoved to the desired positions within actuators 38, 39, and enabling theforces acting on pistons 214, 215 to be balanced to maintain the pistonsin their desired positions. As the current is reduced in valves PCV1 andPCV4, the pressure differential in the hydraulic system is reducedreducing the restriction of fluid flow to reservoir 220 through port T.This allows the lean control system to reduce lean or return the portionof the trike to a centered configuration.

Using hydraulic actuators 38, 39 as discussed affords some majoradvantages to trikes. First, since the lean of the trike 10 iscontrolled by the hydraulic actuators 38, 39, the upper and lowercontrol arms 32, 34, spring dampers 36, and steering components are freeto act normally, regardless of the trikes lean. This allows the trike 10to absorb bumps while tracking an arcuate path in the same manner itwould if it were tracking a straight line, making for a consistentsuspension action, even while turning.

Operation of hydraulic system 200 when actuating auxiliary lean controlsystem 26 will now be discussed with reference to FIGS. 10, 11, and 13.

Referring to the auxiliary lean control system 26, it is mechanicallycontrolled, and is only operable when the trike 10 needs assistancemaintaining an upright position (i.e., when the hydraulic system 200 isno longer able to supply enough pressure to properly utilize thehydraulic actuators 38, 39). Loss of hydraulic system pressure can occurin a number of different ways. When the trike 10 is parked and turnedoff, the hydraulic pump 201 is no longer applying pressure to thehydraulic system 200, so the hydraulic actuators 38, 39 will not becapable of supporting the trike 10. If the hydraulic system 200 fails inany way (i.e. pump failure, ruptured hose, punctured hydraulic actuator,etc.), pressure will also be lost, even if the vehicle engine is stillrunning and the trike 10 is still operable. Yet another potentialfailure could occur if the electronic control system for the hydraulicactuators 38, 39 malfunctions. It should be noted that this list offailure modes is not complete and can include other programmed faults,even unrelated to the hydraulic system. Regardless of how hydraulicpressure is lost, the auxiliary lean control system 26 will return thetrike 10 to an upright and safe position.

FIGS. 10 and 11 are section views of the auxiliary lean control system26 illustrating the trike 10 in a leaning position and an uprightposition, respectively. Since the transverse beam 30 and the cam 138 areboth supported by the keyed shaft 61, they will not rotate with respectto one another. As the trike 10 leans, the transverse beam 30 and thecam 138 remain substantially horizontal. From the perspective of the cam138, the rest of the trike 10 appears to rotate about the keyed shaft61. This is illustrated best in FIG. 10, where it is clear that when thetrike 10 leans, the auxiliary lean control system 26 appears to rotateabout the keyed shaft 61.

As explained above, hydraulic fluid is supplied to centering valve 204.When the primary lean control system is functioning properly, thepressure from the hydraulic fluid in the first cylinder 156 is greaterthan the pressure of the compressed gas in the second cylinder 158. Thisforces the piston 160 downward, and disengages the roller assembly 136from the cam 138, placing the auxiliary lean control system 26 into anunengaged position (FIG. 10). When any of the above mentioned hydraulicsystem failures occur, pressure is also lost to the first cylinder 156.This allows the compressed gas in the second cylinder 158 to expand andpush the piston 160 up, placing the auxiliary lean control system 26into an engaged position, where the roller assembly 136 is in contactwith the cam 138 (FIG. 11). The pressure from the compressed gas islarge enough that the center roller 176 pushes on the inner profile ofone of the cam lobes 182 with enough force to drive the center roller176 into the cam recess 180, bringing the trike 10 to an uprightposition. As long as the hydraulic system is not pressurized, thepressure in the second cylinder 158 will be greater than the pressure inthe first cylinder 156. This will keep the center roller 176 engagedwith the cam roller recess 180 and will prevent the trike 10 fromleaning.

In the event that a failure occurs other than hydraulic system pressureloss, the electronic control unit (ECU) ( FIG. 13) controlling thehydraulic system 200 is capable of eliminating hydraulic fluid pumping,and thus hydraulic pressure. This also relieves the pressure in thefirst cylinder 156, allowing the auxiliary lean control system 26 tofunction. When the hydraulic system is pressurized again, the pressurein the first cylinder 156 will again be greater than the pressure in thesecond cylinder 158. This forces the piston 160 downward, disengagingthe roller assembly 136 from the cam 138 and allowing the bike 10 tofunction normally.

The embodiment just described is adapted for bringing a portion of thetrike to a lean angle of approximately zero degrees (corresponding to anupright position) when the trike resides on a substantially level roadsurface. In this case, piston 160 forces roller assembly 136 torollingly engage the contoured surface of cam 138 until the rollerassembly is centered along the contoured surface of the cam. The rollersbecome nested and locked within the grove formed in the cam surface whena lean angle of approximately zero degrees is achieved. Pressure appliedby piston 160 holds the rollers in place, which locks the auxiliary leancontrol system in the zero-degree lean angle configuration and preventsthe vehicle from leaning away from this position, thereby providing anupright vehicle configuration having a relatively low potential energy.

FIG. 12 shows a resultant potential energy function derived by applyingthe energy stored in the second lean control system to bring the vehiclebody to an upright configuration in which the lean angle toapproximately zero (on a substantially level road surface), effectivelycombining the potential energy function shown in FIG. 7 with thepotential energy function shown in FIG. 8. In addition, when the vehiclebody is brought to an upright position, the vehicle body is locked inthe upright position by the auxiliary lean control system to prevent thevehicle body from leaning in either lateral direction while the firstlean control system is non-functioning and while the second lean controlsystem is engaged. It may be seen from FIG. 3 that the uprightconfiguration of the vehicle with the leaning suspension system lockedin a zero or near-zero lean angle configuration is a relatively stableconfiguration of the vehicle, since a non-zero vehicle lean angle mayonly be achieved by tilting or rolling the entire vehicle, therebycreating a vehicle configuration at a state of relatively higherpotential energy than that provided by the upright, zero lean-angleconfiguration.

The shape of the auxiliary system potential function of FIG. 8 may becontrolled by a combination of energy storage device internal pressureand system mechanics (cam dimensions, etc.). The optimum shape of thefunction will be determined by factors such as the configuration of thevehicle upon deactivation or malfunction of the primary lean controlsystem, and the desired final configuration of the vehicle. A potentialfunction representing the final vehicle configuration (and combining thepotential functions shown in FIGS. 7 and 8) is shown in FIG. 12. Theshape of the combined function in any particular application will bedetermined by the desired final configuration of the vehicle.

If a failure occurs other than hydraulic system pressure loss, the ECU217 is capable of eliminating hydraulic fluid pumping, and thushydraulic pressure. This also relieves the pressure in the firstcylinder 156, allowing the auxiliary lean control system 26 to function.When the hydraulic system 200 is pressurized again, the pressure in thefirst cylinder 156 will again be greater than the pressure in the secondcylinder 158. This forces the piston 160 downward, disengaging theroller assembly 136 from the cam 138 and allowing the trike 10 tofunction normally.

Referring again to FIG. 13, a hydraulic system failure may occur inwhich hydraulic fluid is trapped in the hydraulic lines between eitherhydraulic actuator chambers 210 and 213, or in the hydraulic linesbetween chambers 211 and 212. This could occur if, for example, the ECU217 malfunctions and doesn't allow valves PCV3 or PCV4 to open. If thisoccurs, the hydraulic actuators 38, 39 may become locked in whatevertheir current state is, thereby possibly locking the trike in a leaningposition. This would prevent the auxiliary lean control system 26 fromoperating, as the auxiliary lean control system is incapable of exertingenough force to overcome the force exerted on the transverse beam 30 bythe trapped hydraulic fluid. To remedy this situation, the centeringenable valve 206 is opened when the centering valve 204 is opened. Thisallows hydraulic fluid to flow between any of the hydraulic actuatorchambers 210-213 and prevents any hydraulic fluid from getting trappedbetween the hydraulic actuators 38, 39.

From the above description, it may be seen that the hydraulic system ofthe present invention includes a plurality of actuators for combining toprovide a selected configuration of a vehicle, wherein the selectedconfiguration of the vehicle comprises either a first configuration of aplurality of first configurations or a second configuration of aplurality of second configurations. In the embodiment described above,the selected configuration of the vehicle defines a lean angle of atleast a portion of the vehicle. The hydraulic system also includes afirst hydraulic circuit adapted for energizing the plurality ofactuators to produce a first configuration of the plurality of firstconfigurations of the vehicle when the first hydraulic circuit isactivated. The hydraulic system also includes a second hydraulic circuitadapted for energizing the plurality of actuators to produce a secondconfiguration of the plurality of second configurations of the vehiclewhen the second hydraulic circuit is activated.

The first hydraulic circuit includes the hydraulic lines, valves, etc.defining a flow path of the hydraulic fluid required to cause theactuators to operate so as to lean the vehicle to the right. Similarly,the second hydraulic circuit includes the hydraulic lines, valves, etc.defining a flow path of the hydraulic fluid required to cause theactuators to operate so as to lean the vehicle to the left. As the firstand second hydraulic circuits are never both activated simultaneously,portions of the hydraulic system may be common to both the first andsecond hydraulic circuits. In alternative embodiments (not shown), thefirst and second hydraulic circuit may be constructed so as toincorporate no common elements.

A control system (in the embodiment described above, ECU 217) isoperatively coupled to both the first hydraulic circuit and the secondhydraulic circuit for selectively activating one of the first hydrauliccircuit and the second hydraulic circuit to provide, responsive to atleast one input to the control system, one of a respective firstconfiguration of the plurality of first configurations of the vehicle orone of a respective second configuration-of the plurality of secondconfigurations of the vehicle, wherein the first configuration of thesecond configuration provided by the actuators corresponds to theselected configuration of the vehicle.

Unless otherwise noted, elements of the vehicle lean control systems andhydraulic system described herein may be fabricated and interconnectedusing methods known in the art. It will also be understood that theforegoing descriptions of embodiments of the present invention are forillustrative purposes only. As such, the various structural andoperational features herein disclosed are susceptible to a number ofmodifications commensurate with the abilities of one of ordinary skillin the art, none of which departs from the scope of the presentinvention as defined in the appended claims.

1. A hydraulic system comprising: a plurality of actuators operativelycoupled to a vehicle for providing a desired configuration of thevehicle; and a valve system operatively coupled to the plurality ofactuators for controlling a flow of pressurized fluid to the pluralityof actuators to energize the plurality of actuators to provide,responsive to the desired configuration of the vehicle, a firstconfiguration of a plurality of first configurations of the vehiclecorresponding to the desired configuration of the vehicle, or a secondconfiguration of a plurality of second configurations of the vehiclecorresponding to the desired configuration of the vehicle.
 2. Thehydraulic system of claim 1 wherein the desired configuration of thevehicle defines a lean angle of at least a portion of the vehicle. 3.The hydraulic system of claim 1 wherein the plurality of firstconfigurations comprises a plurality of rightward lean angles of atleast a portion of the vehicle, and wherein the plurality of secondconfigurations comprises a plurality of leftward lean angles of at leasta portion of the vehicle.
 4. The hydraulic system of claim 1 furthercomprising an electronic control system for generating, responsive tothe desired configuration of the vehicle, a control signal forcontrolling the valve system to control the flow of the pressurizedfluid.
 5. The hydraulic system of claim 1 wherein the plurality ofactuators comprises a first hydraulic cylinder including a first fluidchamber, a second fluid chamber, and a first movable element positionedbetween the first chamber and the second chamber to separate the firstand second chambers; and a second hydraulic cylinder including a thirdfluid chamber, a fourth fluid chamber, and a second movable elementpositioned between the third chamber and the fourth chamber to separatethe third and fourth chambers, and wherein the first and second movableelements are movable in response to a flow of the pressurized fluid intothe plurality of actuators.
 6. The hydraulic system of claim 5 whereinthe first configuration of the plurality of first configurations of thevehicle is provided by controlling a flow of the pressurized fluid intothe plurality of actuators o as to move the first movable element in afirst direction and the second movable element in a second directionsubstantially opposite the first direction, and wherein the secondconfiguration of the plurality of second configurations of the vehicleis provided by controlling a flow of the pressurized fluid into theplurality of actuators so as to move the first movable element in thesecond direction and the second movable element in the first direction.7. The hydraulic system of claim 5 wherein the valve system includes afirst valve element, a second valve element, a third valve element, anda fourth valve element, wherein the first valve element and the fourthvalve element are simultaneously controlled to control the flow of thehydraulic fluid to control a pressure differential between the first andsecond chambers to move the first movable element in a first directionand to control a pressure differential between the third and fourthchambers to move the second movable element in a second direction, tomove the vehicle into the first configuration of the plurality of firstconfigurations; and wherein the second valve element and the third valveelement are simultaneously controlled to control the flow of thehydraulic fluid to control a pressure differential between the first andsecond chambers to move the first movable element in the seconddirection, and to control a pressure differential between the third andfourth chambers to move the second movable element in the firstdirection, to move the vehicle into the second configuration of theplurality of second configurations.
 8. The hydraulic system of claim 7wherein the valve elements comprise proportional control valves.
 9. Thehydraulic system of claim 8 wherein the valve elements comprisesolenoid-actuated spool valves.
 10. The hydraulic system of claim 7wherein the valve elements are incorporated into a single valve block.11. The hydraulic system of claim 10 wherein the valve block furtherincludes a fifth valve element adapted to substantially equalize fluidpressure in a portion of the hydraulic system supplying fluid to theplurality of actuators and a portion of the hydraulic system conveyingfluid from the plurality of actuators when the hydraulic system is notenergized.
 12. The hydraulic system of claim 1 wherein the hydraulicsystem is incorporated into a vehicle for controlling a lean angle of atleast a portion of the vehicle, the plurality of first configurations ofthe vehicle define a corresponding plurality of first lean angles of atleast a portion of the vehicle, and wherein the plurality of secondconfigurations of the vehicle define a corresponding plurality of secondlean angles of at least a portion of the vehicle.
 13. The hydraulicsystem of claim 1 wherein the hydraulic system further comprises a valveelement adapted to substantially equalize fluid pressure in a portion ofthe hydraulic system supplying fluid to the plurality of actuators and aportion of the hydraulic system conveying fluid from the plurality ofactuators when the hydraulic system is not energized.
 14. The hydraulicsystem of claim 1 further comprising: a hollow cylinder formed within ahousing; a piston slidably positioned within the cylinder and adapted toform a substantially fluid-tight seal between a first portion of thecylinder proximate a first end of the piston and a second portion of thecylinder proximate a second end of the piston; and a compressible fluidpositioned within the first portion of the cylinder between the firstend of the piston and a first end of the cylinder, and wherein apressurized fluid resides within the second portion of the cylinder forexerting a force on the piston to compress the compressible fluidpositioned within the first portion of the cylinder when the hydraulicsystem is energized.
 15. A vehicle including a hydraulic system inaccordance with claim
 1. 16. A hydraulic system comprising: a pluralityof actuators operatively coupled to a vehicle for combining to provide aselected configuration of the vehicle, the selected configuration of thevehicle comprising one of a first configuration of a plurality of firstconfigurations and a second configuration of a plurality of secondconfigurations of the vehicle; a first hydraulic circuit adapted forenergizing the plurality of actuators to provide the first configurationof the plurality of first configurations of the vehicle when the firsthydraulic circuit is activated; a second hydraulic circuit adapted forenergizing the plurality of actuators to provide the secondconfiguration of the plurality of second configurations of the vehiclewhen the second hydraulic circuit is activated; and a control systemoperatively coupled to the first hydraulic circuit and the secondhydraulic circuit for selectively activating one of the first hydrauliccircuit and the second hydraulic circuit to provide, responsive to atleast one input to the control system, the first configuration of theplurality of first configurations of the vehicle or the secondconfiguration of the plurality of second configurations of the vehicle,corresponding to the selected configuration of the vehicle.
 17. Thehydraulic system of claim 16 further comprising a valve element adaptedto substantially equalize fluid pressure in a portion of the hydraulicsystem supplying fluid to the plurality of actuators and a portion ofthe hydraulic system conveying fluid from the plurality of actuatorswhen the hydraulic system is not energized.
 18. A vehicle including ahydraulic system in accordance with claim
 16. 19. The hydraulic systemof claim 16 further comprising: a hollow cylinder formed within ahousing; a piston slidably positioned within the cylinder and adapted toform a substantially fluid-tight seal between a first portion of thecylinder proximate a first end of the piston and a second portion of thecylinder proximate a second end of the piston; a compressible fluidpositioned within the first portion of the cylinder between the firstend of the piston and a first end of the cylinder; and a pressurizedfluid positioned within the second portion of the cylinder for exertinga force on the piston to compress the compressible fluid positionedwithin the first portion of the cylinder when the hydraulic system isenergized.
 20. A hydraulic system comprising: a hollow cylinder formedwithin a housing; an actuator slidably positioned within the cylinderand adapted to form a substantially fluid-tight seal between a firstportion of the cylinder proximate a first end of the actuator and asecond portion of the cylinder proximate a second end of the actuator; acompressible fluid positioned within the first portion of the cylinderbetween the first end of the actuator and a first end of the cylinder;and a pressurized hydraulic fluid positioned within the second portionof the cylinder for exerting a force on the actuator to compress thecompressible fluid positioned within the first portion of the cylinderwhen the hydraulic system is energized.
 21. The hydraulic system ofclaim 20 wherein the actuator is maintained in a first position when thehydraulic system is energized, and wherein the compressible fluidexpands to move the actuator from the first position to a secondposition when the hydraulic system is unenergized.